The present invention relates generally to ophthalmic microsurgical instruments and more specifically, but not by way of limitation, to microsurgical instruments suitable for creating a corneal pocket incision for the implantation of intracorneal optical lenses (ICOLs).
The human eye in its simplest terms functions to provide vision by transmitting light through a clear outer portion called the cornea, and focusing the image by way of a crystalline lens onto a retina. The quality of the focused image depends on many factors including the size and shape of the eye, and the transparency of the cornea and the lens.
The optical power of the eye is determined by the optical power of the cornea and the crystalline lens. In the normal, healthy eye, sharp images are formed on the retina (emmetropia). In many eyes, images are either formed in front of the retina because the eye is abnormally long (axial myopia), or formed in back of the retina because the eye is abnormally short (axial hyperopia). The cornea also may be asymmetric or toric, resulting in an uncompensated cylindrical refractive error referred to as corneal astigmatism. In addition, due to age-related reduction in lens accommodation, the eye may become presbyopic resulting in the need for a bifocal or multifocal correction device.
In the past, axial myopia, axial hyperopia and corneal astigmatism generally have been corrected by spectacles or contact lenses, but there are several refractive surgical procedures that have been investigated and used since 1949. Barraquer investigated a procedure called keratomileusis that reshaped the cornea using a microkeratome and a cryolathe. This procedure was never widely accepted by surgeons. Another procedure that has been used is radial and/or transverse incisional keratotomy (RK or AK, respectively). Photoablative lasers have also been used to reshape the surface of the cornea (photorefractive keratectomy or PRK) or for mid-stromal photoablation (Laser-Assisted In Situ Keratomileusis or LASIK). All of these refractive surgical procedures cause an irreversible modification to the shape of the cornea in order to effect refractive changes, and if the correct refraction is not achieved by the first procedure, a second procedure or enhancement must be performed. Additionally, the long-term stability of the correction is variable because of the variability of the biological wound healing response between patients.
Permanent intracomeal implants made from synthetic materials are also known for the correction of corneal refractive errors. Such implants may be generally classified into two categories.
One category is intracorneal implants that have little or no refractive power themselves, but change the refractive power of the cornea by modifying the shape of the anterior surface of the cornea. U.S. Pat. No. 5,123,921 (Werblin, et al.); U.S. Pat. Nos. 5,505,722, 5,466,260, 5,405,384, 5,323,788, 5,318,047, 5,312,424, 5,300,118, 5,188,125, 4,766,895, 4,671,276 and 4,452,235 owned by Keravision and directed to intrastromal ring devices; and U.S. Pat. No. 5,090,955 (Simon), U.S. Pat. No. 5,372,580 (Simon, et al.), and WIPO Publication No. WO 96/06584 directed to Gel Injection Adjustable Keratoplasty (GIAK) all disclose examples of this category of implant.
A second category is intracomeal implants having their own refractive power. U.S. Pat. No. 4,607,617 (Choyce); U.S. Pat. No. 4,624,669 (Grendahl); U.S. Pat. No. 5,628,794 (Lindstrom); and U.S. Pat. Nos. 5,196,026 and 5,336,261 (Barrett, et al.) provide several examples of this category. In addition, U.S. patent application Ser. No. 08/908,230 filed Aug. 7, 1997 entitled xe2x80x9cIntracomeal Diffractive Lensxe2x80x9d, which is incorporated herein in its entirety by reference, discloses an example of an ICOL that has both refractive and diffractive powers.
Microsurgical instruments used for the implantation of such intracorneal implants have also been developed. For example, WIPO Publication No. WO 99/30645 owned by Keravision discloses a variety of instruments for surgically implanting ring-shaped intracorneal implants and ICOLs. These tools may be used manually, but are preferably used in cooperation with a vacuum centering device. The surgical procedures described in this publication require multiple instruments to form an intracomeal ring-shaped channel or an intracomeal pocket. In addition, the use of a vacuum centering device increases the expense of the surgical procedure.
Accordingly, a need exists for a microsurgical instrument that more effectively creates an intracomeal pocket for the implantation of an ICOL. The instrument should be easy for the surgeon to use, should maximize patient safety, and should be economically feasible. The instrument should eliminate the need for multiple tools for forming the intracorneal pocket.
A preferred embodiment of the present invention is an ophthalmic microsurgical instrument that includes a handle and a dissecting tip coupled to the handle. The tip includes a blade having a generally elliptical three-dimensional geometry. The blade may include an edge having a first arc and an opposing second arc. When the instrument is used to form an intracorneal pocket, the curvature of the first arc allows the edge to dissect a first blind spot of the pocket, and the curvature of the second arc allows the edge to dissect a second blind spot of the pocket. The blade may also be formed with a first depression in its top surface and a second depression in its bottom surface. When the instrument is used to form an intracomeal pocket, the depressions reduce the drag on, and corresponding trauma to, stromal tissue.